Muscle it up: Ball Curls

For week one, sit on the ball with legs and feet close together, toes just touching the floor. Do three sets of biceps curls (12—15 reps), using 5- to 8-pound weights. For week two, do curls while sitting on the ball, feet off the ground. In week three, kneel on the ball and do three sets of 30-second intervals (use a nearby wall for balance). Once you're comfortable and steady, add the biceps curl. Keller suggests starting with one dumbbell, so you can catch yourself with the other hand if you start to teeter. Increase weight as you get stronger.